@Service
public class CommentService {
    private final CommentMapper commentMapper;
    private final ReplyMapper replyMapper;
    private final AnswerMapper answerMapper;

    @Autowired
    public CommentService(CommentMapper commentMapper,
                          ReplyMapper replyMapper,
                          AnswerMapper answerMapper) {
        // ...
    }

    public List<Comment> getCommentUnderAnswer(Long answerId) {
        // ...
        return commentMapper.selectList(commentQueryWrapper);
    }
    // ...
}
